In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium to form characters and images. The ink-jet printing methods have been rapidly spread because of their various advantages such as easiness of full coloration, low costs, capability of using plain paper as the recording medium, non-contact with printed images and characters, etc.
Patent Document 1 discloses an ink for ink-jet printing which includes at least a coloring material, an organic solvent, water and a polymer compound wherein a content of water in the ink is from 10 to 50% by mass, a content of the water-soluble organic solvent having an SP value of from 9.0 to 12.0 in the ink is 30% by mass or more, and the polymer compound contains a plurality of side chains which are bonded to a hydrophilic main chain thereof and can be crosslinked to each other by irradiation with active energy rays. In Patent Document 1, it is described that the ink is excellent in ejection stability and anti-curling property.
Patent Document 2 discloses a process for producing an aqueous pigment dispersion by using a pigment and a resin containing a carboxyl group and a crosslinkable functional group in which the crosslinkable functional group of the resin is reacted with a crosslinking agent. In Patent Document 2, it is described that the resulting aqueous pigment dispersion exhibits a good storage stability and is capable of forming a coating film that is excellent in water resistance, durability, etc.
Patent Document 3 discloses an aqueous pigment dispersion including a carboxyl group-containing thermoplastic resin and a pigment dispersed in the thermoplastic resin wherein the carboxyl group-containing thermoplastic resin is crosslinked after dispersing the pigment therein. In Patent Document 3, it is described that the aqueous pigment dispersion is excellent in light fastness, water resistance, solvent resistance, stability with time, etc.
Patent Document 4 discloses an ink for jet printers which contains a quinacridone solid solution pigment which is constituted of two or more kinds of quinacridone-based compounds.
Patent Document 5 discloses a water-based ink for ink-jet printing which includes a water dispersion of particles of a water-insoluble vinyl polymer containing a solid solution magenta pigment wherein the water-insoluble vinyl polymer is obtained by copolymerizing at least (A) an alicyclic (meth)acrylate and (B) a salt-forming group-containing monomer.
Patent Document 6 discloses an aqueous pigment dispersion for ink-jet printing which is obtained by kneading a mixture of a quinacridone solid solution pigment, a salt-forming group-containing polymer, a neutralizing agent, an organic solvent and water and then adding water and/or an organic solvent to the resulting kneaded material to dilute and disperse the material therein.
However, the above conventional aqueous dispersions and water-based inks are still unsatisfactory in storage stability and anti-curling property.
Patent Document 1: JP 2007-91910A
Patent Document 2: JP 9-104834A
Patent Document 3: WO 99/52966A
Patent Document 4: JP 10-219166A
Patent Document 5: JP 2005-29597A
Patent Document 4: JP 2006-104367A